Scott Brown had a great idea in 2012 when he ran for re-election to the U.S. Senate from Massachusetts. His opponent, Elizabeth Warren, agreed and together they signed The People's Pledge to stop third-party advertising in their campaign. That year, Brown encouraged "other candidates across the country to adopt similar agreements in their races to limit the impact of outside special interests."

I very much admired the People's Pledge. I believe it limited the influence of outside groups and allowed the people's voices to be heard. It allowed the candidates to make their best case and voters to decide, without third party advertising drowning them out.

What was a great idea in 2012 is still a great idea in 2014. That's why I've asked Scott Brown to sign the same pledge — his pledge — in this year's U.S. Senate campaign in New Hampshire. Brown is so far refusing to sign, saying it's too late, because third parties already have spent money on advertising in New Hampshire.

It's a phony argument. We are at a very similar moment in this race as when Brown and Warren signed the pledge in January 2012. Third parties already had spent more than $3 million in Massachusetts when Brown and Warren signed the pledge — almost twice as much as what's so far been spent in New Hampshire. In no small measure, that spending is what led to the Pledge. And Warren signed the pledge even though she still faced a Democratic primary months away.

Only a few weeks ago, Scott Brown enthusiastically embraced and endorsed his pledge again. "It worked," he said at Cornell University last month, and he was right then too.

The People's Pledge worked in many important ways.

Common Cause, an independent group aimed at protecting voter rights, examined the impact of The People's Pledge and found the pledge reduced outside spending, so-called "dark" or completely undisclosed money, and negative advertising, and increased public disclosure of contributors and the influence of smaller donors.

The facts in this independent study are clear. Outside spending made up only 9 percent of total spending in Massachusetts, compared to more than 60 percent in the next most expensive races in the country. Contributions of less than $200 outweighed contributions from big donors in the Massachusetts race by three to one: $23.5 million compared to $8 million. In the next most expensive races, big donors outmuscled the small by more than five to one: $135 million to $23.8 million. There was five times more "dark" money in the top spending states than there was in Massachusetts. Negative ads were barely 40 percent of the total in Massachusetts, compared to an average more than twice that: 84 percent in the other races.

The People's Pledge "imposed accountability on the race" and "candidates had to take responsibility for attacks lobbed at their opponents and couldn't hide behind third party groups," The Boston Globe concluded. The People's Pledge, they wrote, is "about preventing the state's next Senator from coming into office beholden to special interests that may or may not be known to voters." It "represented a commitment by both candidates to take ownership of their campaigns."

I am ready to make that commitment and have asked Scott Brown to do the same. As governor and as a U.S. senator, I've worked hard to put New Hampshire first and make a difference for the people I represent. The people of New Hampshire deserve candidates who will take ownership of their campaigns and an election where they can hear the candidates and decide who will best represent their interests.

When Scott Brown signed The People's Pledge in 2012, he said third parties "are not good for the process," and outside spending is "not good for the people of Massachusetts and they deserve better." I believe New Hampshire voters deserve better, and in that spirit, invite Scott Brown again to commit to the standard he set in Massachusetts.